Microsampling air pollution

Michael Heimbinder samples air under the Manhattan Bridge using a sensor and a smartphone app to create air quality maps in New York City | credits: New York Times Service

Near the corner of Tillary and Jay Streets in Brooklyn, Michael Heimbinder stood near a blue mailbox, head down, poking at his smartphone. A graph appeared: a single line plotting ambient carbon monoxide exposure in the neighborhood.

Minutes later, he ran over to an idling Honda Pilot and held a small, black sensor to its tailpipe. On his phone, carbon monoxide levels, predictably, jumped off the chart. A woman opened the car door and said, “Can I help you out?”

“Just sampling air,” Heimbinder said. He gave a quick grin and dashed on to a woman with a lighted cigarette.

Heimbinder, 36, who lives in Park Slope and runs a nonprofit organization called Habitat Map, is a pollution hunter. Armed with a portable sensor attached with Velcro to his biceps, he uses his smartphone to record minuscule fluctuations in air quality.

The system, known as AirCasting, allows him to create and share online color-coded maps of neighborhood air quality. (Hardware components cost as little as $180 – the whole thing is about the size of three smartphones.)

Looking for hazardous air where federal authorities can’t or don’t, he’s bicycled around Newtown Creek and taken samples above the Brooklyn-Queens Expressway.

“You’re not going to be able to tell the difference between clean air and moderately unhealthy air,” he said.

“You can’t see it.”

By at least one metric, the Global Burden of Disease, outdoor particle pollution is among the top 10 risk factors affecting mortality worldwide. Two-thirds of those deaths occur in Asia; 100,000 to 120,000 occur annually in the United States.

The Environmental Protection Agency collects data on carbon monoxide, nitrogen dioxide, ozone, particulate matter, sulfur dioxide and lead at 17 sites in New York City.

The sites are part of a national network of 1,400 stations that monitor pollutants and help the agency issue air quality alerts. But air pollution, except for ozone, is not distributed uniformly across an urban environment. Particulates vary from neighborhood to neighborhood, even from one floor of a building to another.

Now, scientists struggling to understand exactly where and how we’re exposed to air pollution are making use of the nuanced data captured by anyone with a low-cost mobile air sensor.

The EPA plans to include “citizen-collected data” to supplement existing monitoring stations.

“We get inquiries from people all the time, and we’d love to make use of their data,” said Ron Williams, a research chemist at the EPA.

“These technologies really have exploded in the last five years – cellphone-based technologies, wirelessly transmitted data – but we don’t know how well they’re performing.”

Williams recently ran nine sensors (including AirCasting) through an Air Sensor Evaluation and Collaboration program to verify the data quality.

The agency is sharing the results with developers to help them fine-tune their sensors. The so-called “small sensor” movement continues to expand.

The Air Quality Egg released last year and measures outdoor carbon monoxide and nitrogen dioxide; users can buy a monitor rather than building it themselves. Researchers at the University of Colorado Boulder plan to deploy sensors around hydraulic fracturing wells to monitor airborne emissions.

Others are developing creative ways to display information. Last year, two graduate students, Xiaowei Wang and Deren Guler, flew kites fitted with monitors above Beijing, giving a real-time readout of air pollution with flying, blinking LED lights – almost like stars in the hazy night sky.

Researchers say the data can drive changes in everyday behavior. Two years ago, William Griswold, a computer scientist at the University of California, San Diego, handed out portable CitiSense sensors to 16 commuters.

A paper presented at Wireless Health 2012 reported that participants using the sensors found “urban valleys” where buildings trapped pollution.

Bus riders, probably among the lowest contributors to air pollution, nonetheless received high exposures while waiting on busy streets, the sensors found. Passengers in public buses saw higher exposures, too, compared with those in automobiles. (Newer cars have cabin filters that remove ozone and nitrogen dioxide.)

Once they saw the data, Griswold said, “many participants changed their habits. They started walking different streets or driving with windows rolled up.”

Heimbinder’s group will call on AirCasting users to assess air quality around Newtown Creek, the South Bronx and other areas crisscrossed with highways, waste transfer facilities, dry cleaners and other pollution sources that can’t be detected in large-scale monitoring. Beyond prompting changes in daily commutes, Heimbinder said he expected environmental activists to take these observations to lawmakers and regulators.

“I do believe in the power of the group to change policy,” he said.

“If we’re measuring air quality, then we can say, ‘Look, we have real evidence here. You have to do something.’”

Back inside a jury-rigged calibration lab at the New York City College of Technology, he listened as a student, Leroy Williams, explained a test of a new nitrogen dioxide sensor.

Williams said the nitrogen dioxide levels had showed a sharp drop when he brought the sensor indoors. “That would make sense,” Heimbinder said.

“You got two bridges out there.” Until now, the plumes of exhaust billowing from the bridges – from 200,000 vehicles a day – had been all but invisible.

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